Recently, a Multiple Input Multiple Output (MIMO) system has been spotlighted as a wideband wireless mobile communication technology. The MIMO system refers to a system capable of improving data communication efficiency using multiple antennas. The MIMO system may be classified into a space multiplexing scheme and a space diversity scheme, depending on whether or not the same data is transmitted.
The space multiplexing method refers to a scheme for simultaneously transmitting different data via a plurality of transmission antennas so as to rapidly transmit data without increasing system bandwidth. The space diversity scheme refers to a scheme for transmitting the same data via a plurality of transmission antennas so as to obtain transmission diversity. Examples of such a space diversity scheme include a space time channel coding scheme.
In addition, the MIMO technology may be classified into an open loop scheme and a closed loop scheme according to feedback of channel information from a reception side to a transmission side. The open loop scheme includes a Space-Time Trellis Code (STTC) scheme in which a transmission side transmits information in parallel, and a reception side detects a signal using a Zero Forcing (ZF) scheme and a Minimum Mean Square Error (MMSE) scheme repeatedly and obtains transmission diversity and coding gain using a space domain and Bell Laboratories Layered Space-Time (BLAST) for increasing information amount by the number of transmission antennas, or the like. The closed loop scheme includes a Transmit Antenna Array (TxAA) scheme, or the like.
FIG. 1 is a conceptual diagram of a Coordinated Multi-Point (CoMP) of the existing intra eNBs and inter eNBs.
Referring to FIG. 1, intra eNBs 110 and 120 and an inter eNB 130 exist in a multi-cell environment. In a Long Term Evolution (LTE) system, the intra eNB is composed of several cells (or sectors). In general, cells which are physically located at the same location are referred to as intra cells and cells located at different locations are referred to as inter cells. As shown in FIG. 1, a single-cell MIMO user located in a single cell may communicate with one serving cell in one cell (sector), and a multi-cell MIMO user located at a cell boundary may communicate with a plurality of serving eNBs in multiple cells (sectors).
A CoMP system refers to a system for applying improved MIMO transmission in a multi-cell environment so as to improve data transmission efficiency of a user who is located at a cell boundary. If the CoMP system is applied, it is possible to reduce inter-cell interference in a multi-cell environment. If such a CoMP system is used, a terminal may receive common data from multi-cell base stations. In addition, the base stations may simultaneously support one or more terminals MS1, MS2, . . . , and MSK using the same radio frequency resource so as to improve system performance. That is, the base station may perform a Space Division Multiple Access (SDMA) method based on channel status information between the base station and the terminal.
The CoMP scheme may be classified into a joint processing scheme by data sharing and a coordinated scheduling scheme/beamforming scheme.
In the CoMP system, a serving base station and one or more coordinated base stations are connected to a scheduler via a wired or wireless network. The scheduler may operate by receiving channel information of channel status between terminals MS1, MS2, . . . , and MSK.
Next, a random access process will be described.
A terminal performs a random access process, for initial network access, handover, presence of downlink data, scheduling request signal transmission, and the like. By this process, various terminal IDs (UE IDs) which identify the terminals are acquired from a network and will be used for communication with a base station in the future.
First, a process of, at a terminal, performing a random access process in order to initially access a network or to reconfigure a wireless link will be described.
The terminal transmits a preamble for random access. The preamble to be used for random access may be received from an upper layer. At this time, a Random Access-Radio Network Temporary Identity (hereinafter, referred to as “RA-RNTI”) used for random access is acquired by time and frequency resources of the preamble used for random access.
The terminal waits for reception of a Physical Downlink Control Channel (hereinafter, referred to as “PDCCH”) which is Cyclic Redundancy Check (CRC)-masked with an RA-RNTI for a specific time, after transmitting the preamble.
The terminal receives a Physical Downlink Shared Channel (hereinafter, referred to as “PDSCH”) including a temporary Cell-Radio Network Temporary Identity (hereinafter, referred to as “temporary C-RNTI”), after receiving the PDCCH CRC-masked with the RA-RNTI.
The terminal performs the random access process again, if the PDCCH CRC-masked with the RA-RNTI or the PDSCH including the temporary C-RNTI is not received for the specific time.
If the UE successfully decodes the PDCCH CRC-masked with the RA-RNTI and the PDSCH including the temporary C-RNTI, the terminal transmits a message including the temporary C-RNTI to a base station in uplink.
The terminal changes the temporary C-RNTI to a C-RNTI upon successfully receiving the PDCCH CRC-masked with the temporary C-RNTI and confirming the temporary C-RNTI in response to the message transmitted in uplink.
Next, a random access process for handover, determination of presence of downlink data, scheduling request signal transmission and the like will be described.
The terminal transmits a preamble for random access. The preamble to be used for random access may be received from an upper layer. At this time, an RA-RNTI used for random access is acquired by time and frequency resources of the preamble used for random access.
The terminal waits for reception of a PDCCH which is CRC-masked with an RA-RNTI for a specific time, after transmitting the preamble.
The terminal receives a PDSCH including a temporary C-RNTI after receiving the PDCCH CRC-masked with the RA-RNTI.
The terminal performs the random access process again, if the PDCCH CRC-masked with the RA-RNTI or the PDSCH including the temporary C-RNTI is not received for the specific time.
The terminal which receives the PDSCH including the C-RNTI transmits a message including the temporary C-RNTI to a base station in uplink.
In random access for handover or scheduling request signal transmission, the terminal finishes the random access process when receiving the PDCCH CRC-masked with the temporary C-RNTI for uplink transmission within a predetermined time. If downlink data exists, the random access process is finished when any PDCCH CRC-masked with the temporary C-RNTI is received.
Thereafter, the base station CRC-masks the PDCCH with the RNTI of the terminal, scrambles and transmits the PDCCH using a scrambling sequence determined according to a cell ID, and scrambles and transmits the PDSCH using a scrambling sequence determined according to the RNTI of the terminal and the cell ID. Accordingly, in the CoMP system, there is a need for a PDCCH and PDSCH transmission method for scrambling a PDCCH and a PDSCH using a scrambling sequence determined according to a certain cell ID.
As described above, as a Coordinated Multi-Point (CoMP) system has appeared, there is a need for a method of transmitting a physical downlink shared channel in the CoMP system.